antonyms are word opposites (black/white, happy/sad, up/down). one of the student's answers confuses the teacher.

i consider this picture a pure example of the generational gap between the new slang of the internet era and the standard english of older generations.

if the teacher knew the origin of the word 'noob' he/she would probably feel an obligation to mark the word as a mistake -- as not part of 'standard english'.

all languages change over time, though, and intermix. sometimes what was once a slang word becomes part of the standard. sometimes a standard word's definition is changed and it turns into slang and is no longer part of the standard. sometimes words disappear.